FIG. 1 and FIG. 2 show staple portions of conventional pen recorders. Of these figures, FIG. 1 is a partially sectional view indicating the printing condition, while FIG. 2 is a partially sectional view indicating the waiting condition. In these figures, a platen 1 has a recording paper 2 would partially therearound, and a pen 3 is carried by a carriage (not illustrated) and can be moved into contact with the recording paper 2. A return spring 4, for example a plate spring, has one end fixed to the aforementioned carriage and urges the pen 3 away from the recording paper 2. The end tip 5 of pen 3 fits within a hole 6 of the plate spring 4. In addition, a hammer 7 is provided for engaging the rear end portion 8 of the pen 3 to urge the pen into contact with the recorder paper 2, and is supported rotatably by the aforementioned carriage through the pivot 9. A freely rotatable roller 10 is carried by the hammer 7, and a push-lever 11 extends parallel to the axis of the platen 1 in a position to engage the roller 10. This push-lever is caused to rotate, about the pivot 12, for example by a solenoid (not illustrated), to pivot the hammer towards the platen 1 and urge the pen 3 against the recording paper 2.
In the above pen recorder, at the time of printing on the recording paper 2, the push-lever 11 pivots against the roller, as indicated by the arrow 13 of FIG. 1. Simultaneously, the hammer 7 pivots as indicated by the arrow 14 with a pressure caused by the push-lever 11, followed by the pen 3 being pushed towards the recording paper 2 as indicated by the arrow 15, against the resilient force of the plate spring 4. In this way, the pen 3 contacts appropriate portions of the recording paper 2. For example, the carriage carrying the pen 3, plate spring 4, hammer 7, axle 9 and roller 10 may move in the axial direction of platen 1 or the recording pen 2 may be fed in the circumferential direction of the platen 1. Thereby, desired printing is carried out on the recording paper 2 by means of the pen 3. While the carriage is moving, the roller 10 continuously rotates in contact with the push-lever 11, suppressing a sliding resistance between the roller and push-lever 11.
In the waiting condition, the push-lever 11 rotates in the direction indicated by the arrow 16 of FIG. 1 and thereby the push-lever 11 is separated from the roller 10, while the pen 3 moves away from the recording paper by the resilient force of the plate spring 4, that is in the direction indicated by the arrow 17 of FIG. 1. When the pen 3 moves away from the recording paper 2, the hammer 7 pivots as indicated by the arrow 18 of FIG. 1, resulting in the condition as shown in FIG. 2.
In a pen recorder constituted as described above, the contact pressure between the pen 3 and recording paper 2 during printing is determined by the accuracy of positioning the pen 3, namely the amount of movement of the hammer 7 and the amount of rotation of the push-lever 11. In addition, as described above, the push-lever 11 extends longitudinally in the axial direction of the platen 1 and, therefore, it may easily deflect in its longitudinal direction.
Therefore, such conventional pen recorders inevitably encounter the defects that the amount of rotation of hammer 7 may change in accordance with the amount of deflection generated on the push-lever 11, to deteriorate the positioning accuracy of pen 3. The contact pressure of pen 3 to the recording paper 2 thus easily becomes unstable, and the thickness of lines printed by such recording pen 3 fluctuates to lower printing quality.
Moreover, the push-lever 11 of such conventional pen recorder is held in contact with the roller 10 during the printing operation, and, consequently, a sliding resistance is generated between the push-lever 11 and the roller 10. Accordingly, the rate of movement of the carriage is restricted by such sliding resistance, making high speed printing difficult.
Furthermore, such sliding resistance between the push-lever 11 and roller 10 may change in accordance with a deflection generated on the push-lever, as mentioned above, and the rate of movement of the carriage, namely pen feeding rate, easily becomes unstable, resulting in deterioration of the printing quality.